The invention involves an axle-drive block for motor vehicles having a first and a second driven axle which contains a first and a second differential in a housing driven by an engine/transmission block, the first differential distributing the torque fed to it between a first half axle of the first driven axle and the second differential, and the second differential further distributing the torque fed to it between a second half axle of the first driven axle and a power take-off for the second driven axle, the two differentials being spur-gear-type planetary gears with parallel axes, the sun wheels of which are in each case connected in terms of drive to the half axles of the first driven axle, and planet wheels of the two differentials meshing with the common ring gear of said planetary gears, one planet carrier being connected in a rotationally fixed manner to the housing accommodating the two differentials and the other planet carrier being connected in terms of drive to the power take-off for the second driven axle.
An axle-drive block of this type is disclosed in DE 44 18 891 C2. In the latter, owing to the particular design and arrangement of the two differentials, optimum adaptation of the moment distribution ratio is achieved with a minimum outlay on construction. Provided between the driven housing, which contains the two differentials, and the power take-off for the second driven axle is a fluid friction clutch as a longitudinal differential lock. The latter is not only complicated and bulky (for which reason it has to be driven via a hollow shaft and arranged outside the housing of the two differentials), it also has the disadvantage of not being suitable for interaction with brake-force and slip-limiting systems (ABS, ESP). The fluid friction clutch is a lock sensing the rotational speed.
EP 94 870 A1 discloses an axle-drive block, in which two bevel gear differentials are connected in series and, in the first differential, the moment for just one side of the first driven axle is branched off. To totally lock the longitudinal differential, the cages of the two bevel gear differentials can be connected by means of a claw clutch. With this arrangement, neither the desired moment distribution nor a symmetrically acting locking can be obtained. In particular, with only a partial locking by means of friction, an asymmetrical distribution of torque with respect to the longitudinal axis of the vehicle would be produced, which is not allowed.
For compatibility with ABS or ESP and for other reasons concerned with driving dynamics, a torque-sensing lock which carries out its task without an external control action is desired. A lock of this type is specified, for example, also in a torsen differential of particular design, but has an unfavorable behavior in terms of wear.
It is therefore the object of the invention to provide, with a minimum outlay on construction, an automatic locking of the longitudinal differential, with it being possible for the automatic locking which can be obtained to be structurally influenced in such a manner that it is adapted to the requirements in terms of driving dynamics.